1. Field of the Invention
The present invention relates to a wide-band array antenna, particularly relates to a wide-band array antenna for improving the performance of a mobile communication system employing the wide-band code division multiple access (WCDMA) transmission scheme.
2. Description of the Related Art
Smart antenna techniques at the base station of a mobile communication system can dramatically improve the performance of the system by employing spatial filtering in a WCDMA system. Wide-band beam forming with relatively low fractional band-width should be engaged in these systems.
The current trend of data transmission in commercial wireless communication systems facilitates the implementation of smart antenna techniques. Major approaches for the designs of smart antenna include adaptive null steering, phased array and switched beams. The realization of the first two systems for wide-band applications, such as WCDMA requires a strong implementation cost and complexity. On each branch of a wide-band array, a finite impulse response (FIR) or an infinite impulse response (IIR) filter allows each element to have a phase response that varies with frequency. This compensates from the fact that lower frequency signal components have less phase shift for a given propagation distance, whereas higher frequency signal components have greater phase shift as they travel the same length.
Different wide-band beam forming networks have been already proposed in literature. The conventional structure of a wide-band beam former, that is, several antenna elements each connected to a digital filter for time processing, has been employed in all these schemes.
Conventional wide-band arrays suffer from the implementation of tapped-delay-line temporal processors in the beam forming networks. In some proposed wide-band array antennas, the number of taps is sometime very high which complicates the time processing considerably. In a recently proposed wide-band beam former, the resolution of the beam pattern at end-fire of the array is improved by rectangular arrangement of a linear array, but the design method requires many antenna elements which can only be implemented if micro-strip technology is employed for fabrication.